In recent years, as one means for accomplishing a decrease in size and thickness of products, electronic elements such as BGA or CSP have been spread which have a rear-face electrode so as to reduce a mounting area. Since it is difficult to inspect connection portions by the use of optical means at the time of using rear-face electrode elements, another means for assuring qualities is required.
In the past, examples of a method of inspecting the insides of electronic elements have included a radiographic inspection method and an ultrasonic flaw detection method. The radiographic inspection method is very effective for checking a disconnection, short circuit and volume anomaly, but it is not suitable to check the separation or the like of the connection portion. Since ultrasonic waves are reflected from portions varying in acoustic property, the ultrasonic flaw detection method is suitable to check the separation or the like of the connection portion, but the inspection object is immersed in a liquid as an ultrasonic transmission medium and an ultrasonic wave is emitted to and received from the inspection object via the liquid to perform the flaw detection. However, the inspection object is immersed in the liquid and thus an electrode material of the inspection object is eluted to the liquid in an ionic form, whereby the reliability deteriorates and according to the property of immersing the inspection object in the liquid, whereby the ultrasonic flaw detection cannot be performed in a production field.
Japanese Unexamined Patent Application Publication No. 2003-177117 discloses a dry ultrasonic flaw detection method of inspecting an inspection object without immersing the inspection object in a liquid. As shown in FIG. 5, a container 3 is used which has only a bottom surface sealed by a polymer membrane 1 and receives an ultrasonic transmission medium 2 therein. As shown in FIG. 6A, an inspection object element 6 is received inside a connection body 4 by pressing the frame-shaped connection body 4 provided at the bottom of the container 3 on an inspection object substrate 5 and a space between the inspection object substrate 5 and the polymer membrane 1 is depressurized by connecting the inside of the connection body 4 to a depressurization device 7a, thereby bringing the polymer membrane 1 into close contact with the inspection object element 6. Accordingly, an ultrasonic wave is emitted from an ultrasonic probe 8 to the inspection object element 6 via the ultrasonic transmission medium 2 and the polymer membrane 1, and a reflection wave is received at the ultrasonic probe 8 to perform flaw detection.